Acid-base and catalytic properties of Al 2O 3ZnO

Abstract

Alumina-zinc oxide catalysts of various compositions were prepared from their nitrates by coprecipitation and the acidic and basic properties were measured by titrations with n-butylamine and benzoic acid using various indicators. The acidities (the numbers of acid sites) at H 0 = −3.0 and H 0 = −5.6 of Al 2O 3ZnO catalysts prepared from their nitrates, were found to be lower than those of Al 2O 3ZnO catalysts prepared from their chlorides by the same method. With the increase in ZnO content, the acidities per unit surface area decreased monotonously, whereas a maximum basicity was observed on Al 2O 3ZnO (1:1), the highest base strength (p K a ) being 12.2. The activity change for alkylation of phenol with methanol was correlated well with the acidity change and the highest selectivity (almost 100%) for formations of ortho products, o-cresol and 2,6-xylenol, was observed on Al 2O 3ZnO (1:9). Isomerization of 1-butene was suggested to proceed on basic sites on Al 2O 3ZnO catalysts. In isomerization of 3-carene (I), the selectivity for formation of 2-carene (II) was more than 90% over Al 2O 3ZnO (1:9). From poisoning experiments with CO 2 and pyridine, the active sites for formation of 2-carene were concluded to be both acidic and basic sites.